Hydraulic braking device for turbine, turbine equipped with such a device and drilling equipment comprising such a turbine

ABSTRACT

The hydraulic braking device ( 10 ) to be installed in a turbine ( 2 ) provided with a turbine shaft ( 4 ) comprising at least one body ( 12 ) connected to the said turbine shaft ( 4 ). 
     When the said hydraulic braking device ( 10 ) is immersed in a fluid medium, axial rotation of the turbine shaft ( 4 ) about its axis causes a movement of the said at least one body ( 12 ) with respect to the said fluid medium, this movement generating a resisting torque (T) related to the rotation speed of the turbine shaft ( 4 ) through a non-linear relation.

TECHNICAL FIELD

This invention relates to a hydraulic braking device for a turbine,designed to reduce the turbine rotation speed in the case of anoverspeed in order to prevent damage to the machine on which the saidturbine is fitted. It also relates to a turbine equipped with such ahydraulic braking device. It also relates to drilling equipment providedwith a turbine equipped with such a hydraulic braking device.

STATE OF PRIOR ART

A braking device for a turbine used on a drilling tool is already known.Document U.S. Pat. No. 5,517,464 describes an instrument for makingmeasurements during drilling designed to measure a number of drillingparameters at the drilling head and to transmit them to the surface, inthe form of acoustic signals modulated through the drilling fluid. Agenerating turbine supplies the power necessary for the detection ofparameters and transmission of signals. The generating turbine comprisesa rotor rotation speed regulation device that uses an electromagneticcircuit. This electromagnetic regulating device has the disadvantagethat it is complex and that it generates heat that must be dissipated.The braking moment increases linearly with the rotation speed. Thislinear rotation induces a serious disadvantage, since a fairlypronounced and undesirable braking effect can occur, even at rotationspeeds located within a speed range corresponding to normal operation ofthe turbine.

Document U.S. Pat. No. 6,155,328 describes another hydraulic brakingdevice associated with a blind winding and unwinding mechanism. Theblind spindle is connected to a hydraulic brake located inside acompartment containing a viscous fluid. The friction caused by rotationof the brake within the viscous fluid reduces the blind rotation speed.This brake generates a resisting torque that excessively slows down thewinding and unwinding mechanism at moderate speeds.

PRESENTATION OF THE INVENTION

According to a first aspect of the invention, a hydraulic braking deviceis proposed for a turbine in equipment, for example such as drillingequipment, which will reduce the turbine rotation speed to prevent anoverspeed from occurring.

The hydraulic braking device for a turbine, the said turbine beingprovided with a turbine shaft, comprises at least one body connected tothe said turbine shaft. When the said hydraulic braking device isimmersed in a fluid medium, rotation of the turbine shaft about its axiscauses a movement of the said at least one body with respect to the saidfluid medium. This movement generates a resisting torque related to therotation speed of the turbine shaft through a non-linear relation.

In general, this non-linear relation is a quadratic relation, in whichthe resisting torque is a function of the square of the rotation speedof the turbine shaft with respect to the said fluid medium.

In one embodiment, a braking shaft is coupled to the said turbine shaft.This coupling between the turbine shaft and the braking shaft includes aconfiguration in which the two shafts are combined into a single shaft,and a configuration in which the two shafts are coupled through acoupling device.

During use, the braking device is immersed in a fluid medium, which maybe either stagnant or flowing, for example in a pipe. When the turbineshaft rotates about its axis, it starts to rotate the braking shaft thatmay either be coincident with the turbine shaft or distinct from theturbine shaft, about its axis, relative to the said fluid medium. Thebraking shaft transmits energy from the turbine to the at least one bodymentioned above, that causes the desired braking.

The braking device according to the invention may be used on an “axial”type turbine, or an “axial inlet and radial outlet” type turbine, or a“radial inlet and axial outlet” type turbine. It may be located on theupstream or downstream side of the turbine. When it is placed on thedownstream side of the turbine, its presence does not disturb the flowentering into the turbine.

The construction of the device is such that a braking effect is obtainedin the case of a turbine overspeed, in other words when the turbinerotation speed exceeds a predetermined threshold value. Therefore, thebraking device according to the invention makes it possible to regulatethe turbine speed.

There are several advantages of the braking effect produced by thehydraulic braking device according to the invention.

Preventing a turbine overspeed avoids damage to elements from which theturbine is made caused by this excessive rotation speed. Subsequently,if the turbine is connected to an electricity generator, excessiveenergy production can also be avoided.

Preventing a turbine overspeed can prevent damage to elements formingpart of the equipment on which the turbine is installed. The said damagecould be a direct result of the excessive turbine rotation speed, or itcould be an indirect result of a sudden projection of an element formingpart of the turbine into its immediate environment.

According to a second aspect of the invention, a turbine equipped with ahydraulic braking device conform with the first aspect of the inventionis proposed.

According to a third aspect of the invention, drilling equipment isproposed comprising a turbine equipped with a hydraulic braking deviceconform with the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeclearer after reading the detailed description of the invention whichwill be presented through embodiments of the invention provided forillustrative purposes, but in no way limitative, with reference to theattached drawings in which:

FIG. 1 shows a perspective view of a first embodiment of the turbinehydraulic braking device;

FIG. 2 shows a perspective view of a second embodiment of the turbinehydraulic braking device;

FIG. 3 shows a drilling installation that uses drilling equipmentcomprising a turbine equipped with a hydraulic braking device accordingto the invention.

DETAILED PRESENTATION OF THE INVENTION

We have seen above that:

-   -   the hydraulic braking device for a turbine including a turbine        shaft comprises at least one body connected to the said turbine        shaft,    -   when the said hydraulic braking device is immersed in a fluid        medium, rotation of the turbine shaft about its axis causes a        movement of the said at least one body with respect to the said        fluid medium,    -   this movement generates a resisting torque that is related to        the rotation speed of the turbine shaft through a non-linear        rotation,    -   in general, this non-linear relation is a quadratic relation in        which the resisting torque is a function of the square of the        rotation speed of the turbine shaft with respect to the said        fluid medium.

We will firstly describe the non-linear relation between the resistingtorque and the rotation speed of the bodies of the hydraulic brakingdevice, this relation being obtained by use of one of Newton's laws.During rotation of the turbine, in other words when the turbine shaft isrotating about its axis, the resisting torque exerted by each of thebodies on the fluid medium with respect to the rotation axis of thebraking shaft is expressed as follows:T=C _(D) .A.ρ.r ³.(ω_(b)−ω_(f))²,

where:

C_(D) is the drag coefficient of the body along a tangential direction,

A is the projected area of the body along a tangential direction,

ρ is the density of the fluid medium,

r is the effective radius of the body, in other words the distancebetween the rotation axis of the braking shaft and the pressure centerof the body, the said pressure center being the location at which theresultant pressure exerted by the fluid medium on the body is applied,

ω_(b) is the body rotation speed,

ω_(f) is the rotation speed of the fluid medium defined byω_(f)=U_(f)/r, where U_(f) is the average tangential flow speed of thefluid medium.

This resisting torque T increases when (1) the drag coefficient C_(D) ofthe body increases; (2) the effective radius r increases; (3) the squareof the rotation speed of the body with respect to the fluid medium(ω_(b)−ω_(f)) increases.

In one embodiment, the rotation speed ω_(D) of the body is proportionalto the rotation speed ω_(b) of the turbine. This proportionality isexpressed by the relation ω_(b)=k.ω_(t), where k is a proportionalityfactor. Consequently, as long as the rotation speed ω_(t) of the turbineremains less than a given speed threshold, the braking effect cannot befelt significantly, as a result of the quadratic relation. On the otherhand, when the rotation speed ω_(t) of the turbine exceeds this speedthreshold, the difference (ω_(b)−ω_(f)) between the rotation speed ofthe body and the rotation speed of the fluid medium increases. Theresisting torque T increases with the square of this difference in therotation speeds. The braking effect is then felt significantly.

It can also be understood that when several bodies are present, theirresisting torques T are additive, and the braking effect is increased.The value of the speed threshold may be chosen as a function of therequired application, and the braking device may be configured as afunction of the required speed threshold.

The shapes and dimensions of the bodies and the number of bodies arechosen such that a sufficient space is formed around each body so as tominimize the rotation speed ω_(f) of the fluid medium. In an extremecase in which the fluid medium is driven in rotation by action of thebodies, the difference in speeds (ω_(b)−ω_(f)) would be almost zero andconsequently the braking effect will be almost non-existent.

In one embodiment, the braking device comprises a braking shaft coupledto the turbine shaft.

The shapes and dimensions of the bodies, and the layout of the bodieswith respect to the braking shaft, are chosen so as to increase thevalue of the drag coefficient C_(D) and/or the value of the effectiveradius r.

The choice of one or more of these parameters can affect the otherparameters. For example, if the number of bodies is increased, the totalresisting torque T is increased. But in this case, the available spacearound each body is reduced, which increases the value of the rotationspeed ω_(f) of the fluid medium and consequently this tends to reducethe resisting torque T. Therefore, the number of bodies is chosen takingaccount of the dimensions of the bodies and the diameter of the brakingshaft.

Similarly, if the dimensions of the bodies are increased, the projectedarea of the body A is increased which tends to increase the resistingtorque T. But in this case, the available space around each body isreduced, which increases the value of the rotation speed ω_(f) of thefluid medium and consequently tends to reduce the resisting torque T.

One way of increasing the effective radius r of a body withoutoversizing it consists of modifying the connection between the brakingshaft and the said body.

Thus, in one variant embodiment, the body is fixed directly onto thebraking shaft through at least one connecting means composed of a bodyanchor zone. According to another variant embodiment, the body isconnected to the braking shaft through at least one connecting meanscomposed of an additional support. When the said at least one connectingmeans has a streamlined profile, the fluid medium can flow around thebraking shaft along its direction of flow, without being driven inrotation in an exaggerated manner. Subsequently, the effective radius rcan be significantly increased without significantly increasing therotation speed ω_(f) of the fluid medium.

The bodies may be profiled bodies or non-profiled bodies. One advantageof non-profiled bodies is that they increase the drag coefficient C_(D)and consequently the resisting torque T without it being necessary tooversize the bodies.

We will now describe particular embodiments of hydraulic braking devicesaccording to the invention with reference to FIGS. 1 and 2.

With reference firstly to the left part of FIG. 1, an “axial” type ofturbine 2 is shown, comprising a turbine shaft 4 capable of rotatingabout its axis 6 and provided with vanes 8, of which there are five inthe example shown.

Now with reference to the right part of FIG. 1, a first particularembodiment of the braking device 10 is shown. The said braking device 10comprises a braking shaft 14 coaxial with the turbine shaft 4 that isfree to rotate about their common axis 6. Rotation of the shaft 14 aboutthe axis 6 is materialized by the arrow 13. The said braking device 10also comprises bodies 12 fixed directly onto the braking shaft 14through an anchor zone 18. These bodies extend radially from the brakingshaft 14. In the example illustrated, there are two of the said bodies12 and they are identical. They are positioned diametrically oppositeeach other on opposite sides of the braking shaft 14. Each isapproximately in the shape of a parallelepiped plate facing a directionparallel to the axial direction of the braking shaft 14.

In order to facilitate understanding, a local coordinate system (X, Y,Z) is associated with each body 12. It comprises two axes X and Ycontained in the plane of the plate 12 and perpendicular to each other,the X axis being parallel to the rotation axis 6 and the Z axis beingoriented radially outwards. A Y axis completes these axes such that thecoordinate system (X, Y, Z) is a direct orthogonal coordinate system.

The length l of the plates 12 is in the X direction, their width h isalong the Z direction, and the average effective radius r is along the Zdirection. For the plates 12, the area A projected along a tangentialdirection is equal to A=l.h, the tangential direction being the Ydirection.

Now with reference to FIG. 2, a second particular embodiment of thebraking device 10 is shown. It is different from the first embodimentthat was described with reference to FIG. 1 by the fact that each body12 is connected to the braking shaft 14 through a connecting means 20that moves the body 12 away from the braking shaft 14, rather than beingfixed to it directly. In the example shown, the said connecting means 20is in the form of a rigid arm 20 rigidly connected both to the brakingshaft 14 and to the body 12. It is arranged radially, in other wordsalong the normal to the peripheral surface of the braking shaft 14, andis centered with respect to the dimension of the body 12 along the Xdirection.

One variant embodiment of the first embodiment or the second embodimentof 15 the braking device 10 is illustrated in FIG. 1. According to thisvariant, the braking device 10 also comprises a coupling device 50 tocouple the braking shaft 14 with the turbine shaft 4. This couplingdevice 50, shown as a chain dotted line in FIG. 1, may for example be agearbox, or a clutch.

In the presence of a coupling device 50, rotation of the braking shaft14, in other words the rotation speed ω_(b) of the bodies 12 about theaxis 6, is proportional to the rotation speed ω_(t) of the turbine shaft4 about the axis 6, in other words the rotation speed of the turbine 2.The proportionality factor k between the rotation speed of the turbine 2and the rotation speed of the bodies 12 is defined by thecharacteristics of the coupling device 50.

On the other hand, if there is no coupling device 50, the two shafts 4and 14 are coincident and rotate at the same speed about the axis 6.

The turbine braking device 10 is not limited to the examples that havejust been described.

A braking device 10 could be considered with a braking shaft 14 parallelto the turbine shaft 4 without being coaxial with it. In this case, thecoupling device is adapted accordingly to transmit the rotation movementfrom the turbine shaft 4 to the braking shaft 14.

It would be possible to consider a braking device with a number ofbodies not equal to two. For example, it would be possible to consider abraking device comprising a single body. A configuration with severalbodies, in other words at least two, for example three or four or morebodies, would be better than a configuration with a single body, ifthere are any vibrations.

Bodies 12 could be considered in the form of plates that are notparallelepiped shaped, for example polygonal, circular or ellipticalplates, etc.

It would be possible to consider bodies 12 in the form of platesoriented such that their plane is not parallel to the axial direction ofthe braking shaft.

It would be possible to consider bodies 12 in a form other than a plate.In the case of a braking device 10 that will be installed on an “axial”type turbine, it would be possible to consider bodies 12 with anincreased surface area facing the flow direction of the fluid medium.One possible example is the example of a cup-shaped body 12 or with a“V” profile, which would be arranged such that the concave side of eachbody is oriented to face the flow direction of the fluid medium. Onepossible example is the example of a body 12 with a shape approximatelythe same as the shape of the vanes of a Pelton type turbine.

It would be possible to consider bodies 12 with different shapes. Itwould be possible to consider bodies 12 that do not all have the samedimensions.

It would be possible to consider a non-symmetrical distribution of thebodies 12 around the braking shaft 14.

It would be possible to consider an arrangement of bodies with respectto the braking shaft in which the bodies are not all in the same axialposition with respect to the braking shaft.

It can be understood that the use of this type of arrangement of thebraking device and/or combinations between different arrangements canincrease the drag coefficient C_(D) and/or increase the effective radiusr and/or reduce the fluid rotation speed ω_(f), in order to increase thevalue of the resisting torque T.

The invention also relates to a turbine 2 equipped with a hydraulicbraking device 10 according to the invention.

In one particular embodiment, the turbine 2 and the braking device 10are immersed in the same fluid medium.

In another particular embodiment, the turbine 2 is immersed in a firstfluid medium contained in a first containment, and the braking device 10is immersed in a second fluid medium contained in a second containment.The two fluid media can then be chosen to be identical or different.

This turbine may be installed in drilling equipment or a drillinginstallation.

FIG. 3 illustrates the general layout of a drilling installation, whichcomprises a turbine 2 fitted with a hydraulic braking device 10according to the invention. A drilling fluid 101 contained in areservoir 114 is injected using a pump 104 from the surface 102, insidea string of drilling rods 103 that will be used for drilling in ageological formation 107. The drilling fluid 101 reaches a drilling tool105 that terminates the string of drilling rods 103. The drilling fluid101 comes out of the rods string 103 and returns to the surface 102through the space 106 between the rods string 103 and the geologicalformation 107. The path followed by the drilling fluid 101 isillustrated by arrows.

One of the rods 103.1 in the string of drilling rods 103 located closeto the drilling tool 105 is instrumented. This rod contains at least onemeasurement device 108. When it is intended to evaluate the physicalproperties of the geological formation 107, such as its density,porosity, resistivity, etc., this measurement device 108 is known as a“logging while drilling” (LWD) tool. When it is intended to measuredrilling parameters such as the temperature, pressure, orientation ofthe drilling tool, etc., this measurement device 108 is known as a“Measuring While Drilling” (MWD) tool.

The instrumented rod 103.1 is usually a drill collar. This instrumentedrod 103.1 usually comprises a turbine 2, itself equipped with ahydraulic braking device 10 according to the invention.

In a manner known in itself, a flow straightening device may be providedon the upstream side or downstream side of the braking device 10,preferably between the turbine 2 and the braking device 10. The role ofthis flow straightening device is to reduce rotation of the fluid mediumdue to rotation of the turbine 2.

If the assembly consisting of the turbine 2 and the braking device 10 isinstalled in a pipe, the fluid straightening device may for example beformed of complementary bodies fixed to the wall of the pipe.

If this assembly is placed in a fluid medium without being close to anypipe, the flow straightening device may for example be formed ofcounter-vanes located close to the braking device 10.

1. A drilling apparatus comprising: a turbine provided with a turbineshaft, a hydraulic braking device configured to operate with theturbine, wherein the hydraulic braking device consists of a brakingshaft coupled to the turbine shaft and bodies rotatably connected to thebraking shaft, and wherein when the hydraulic braking device is immersedin a drilling fluid, an axial rotation of the turbine shaft causes anaxial rotation of the braking shaft which in turn causes a movement ofthe bodies with respect to the drilling fluid, this movement generatinga resisting torque that is a function of the square of the rotationspeed of the turbine shaft with respect to the drilling fluid providinga quadratic relation, and wherein the construction of the hydraulicbraking device is such that a braking effect is obtained when therotation speed of the turbine shaft exceeds a predetermined thresholdvalue and the braking effect is not obtained when under thepredetermined value as a result of the quadratic relation.
 2. Thedrilling apparatus according to claim 1, wherein the braking shaft iscoaxial with the turbine shaft.
 3. The drilling apparatus according toclaim 1, wherein the braking shaft and the turbine shaft are combinedinto a single shaft.
 4. The drilling apparatus according to claim 1,wherein the bodies are rigidly connected to the braking shaft through aconnecting means.
 5. The drilling apparatus according to claim 1,wherein the bodies are fixed directly onto the braking shaft through aconnecting means composed of at least one anchor zone of the bodies. 6.The drilling apparatus according to claim 1, wherein the bodies aredistributed around the periphery of the braking shaft, in a regularmanner, or in a non-regular manner.
 7. The drilling apparatus accordingto claim 1, wherein the bodies have either all the same axial positionsalong the braking shaft, or different axial positions along the brakingshaft.
 8. The drilling apparatus according to claim 1, wherein thebodies are chosen to be identical or different.
 9. The drillingapparatus according to claim 1, wherein the bodies all have the samedimensions.
 10. The drilling apparatus according to claim 1, wherein thehydraulic braking device is arranged on the downstream side of theturbine with respect to a flow direction of the drilling fluid.
 11. Thedrilling apparatus according to claim 1, wherein the bodies extend alonga length of the braking shaft.
 12. The drilling apparatus according toclaim 1, wherein the bodies extend in a substantially normal directionfrom the braking shaft.
 13. The drilling apparatus according to claim 1,wherein a flow of the drilling fluid drives the turbine.
 14. Thedrilling apparatus according to claim 13, wherein the flow is parallelto a central axis of the braking shaft and to a length of the bodies.15. The drilling apparatus according to claim 1, wherein the turbineshaft and the braking shaft are coupled by a coupling device so that therotation speed of the braking shaft is proportional to but differentfrom the rotation speed of the turbine shaft.
 16. The drilling apparatusaccording to claim 1, wherein the bodies comprise at least onecup-shaped or V-shaped body that is arranged such that the concave sideof the at least one cup-shaped or V-shaped body is oriented to face aflow direction of the drilling fluid.